The present invention relates to a rotary cutting tool such as an end mill, a reamer or the like in which cutting parts formed of a blade material such as a cemented carbide alloy, a high-speed steel or the like are secured to a cutter body i.e., blade rest which is generally formed of steel by means of welding or in any other mechanical manner, and more particularly to the configuration of cutting material which serves as a cutting part.
Blades for use as the cutting part of a rotating cutting tool are classified as being of two types; straight blades and helical blades, the differences being clearly visible when looking at the edges of the relevant blades, in other words, the cutting parts, in the axial direction. Both types of cutting parts are conventionally formed such that the cross sectional configurations thereof are rectangular. With such a cutting part, the rake face thereof is parallel to its opposite face. These features inherent to the conventional cutting parts result from the convenience of manufacturing them in this form. When producing these types of cutting parts using, for instance, cemented carbide alloy, in the case of straight blades, raw material in the form of a powder is pressure molded, is then cut into a rectangular parallelopipedon by means of a diamond grinder or the like, and is finally sintered. On the other hand, in the case of helical blades, raw material in the form of a powder is pressure molded in a helically formed mold, or a straight blade formed as described above can instead be reheated and forced into a metal mold with a helical form. Using this method of manufacture, the rake face can easily be constructed to be parallel to its opposite face.
It is also easy to manufacture a high-speed steel cutting part having the same cross sectional configuration as the one described above, in other words, a cutting part in which the rake face is constructed to be parallel to its opposite face. Almost all of the cutting parts currently used have such a cross sectional configuration.
As described heretofore, in the cutting parts Io, IIo - - - of a known rotary cutting tool, the rank faces (ab, a'b', --) are, as shown in FIGS. 6 to 8, substantially parallel to their opposite faces (cd, c'd', - - - ). In a tool To having such cutting parts, the proximal portion of a steel blade rest Po on which the cutting parts are secured, i.e. the portion (cb') defined between a first cutting part Io and a second cutting part IIo, for instance, tends to become narrower, the rigidity of the tool itself thus being diminished. In addition, when the rake face of the known cutting part is re-ground as indicated by dotted lines a.sub.1 b.sub.1, a.sub.2 b.sub.2, a.sub.3 b.sub.3, the thickness (ad) at the outer peripheral portion of the re-ground cutting part becomes smaller than the thickness (bc) at the inner peripheral portion thereof, thus making it impossible to use the blade material efficiently without any waste.